Designers of ballistic weapons have improved designs in propellants, projectile chambers, and muzzles to improve speed, distance, and accuracy of a projectile fired from the ballistic weapon. However, with these improvements, temperature, friction, and inertia generated within the ballistic weapon during firing have become problems. Solving these problems has been difficult since the problems have interrelated consequences. At best, a compromise between these problems has been achieved.
As the projectile is fired from the ballistic weapon, particles of the projectile are deposited on the barrel of the ballistic weapon due to friction, which fouls the barrel. A majority of projectiles are formed from lead or a leaded alloy, which are suitable for low speed (less than approximately 1000 ft/sec), black powder-type ballistic weapons. However, even in low speed ballistic weapons, frequent cleaning is needed to remove the deposits. Fouling and failure of rifle barrels is also problematic, especially in military use where the integrity of the barrel is pushed to its limits. It is estimated that during firing of a rifle, the temperature within the barrel exceeds 3000° C. and the pressure exceeds 50,000 psi. These temperatures and pressures create cracking, wear, and erosion within the barrel, which greatly reduces its lifetime. As the barrel wears, the range and accuracy of the fired projectile are decreased. In addition, wear in the barrel causes fuse malfunctions, rifling stripping due to torsional impulse, propellant gas blow-by, and excessive muzzle flash. Therefore, the worn barrel must be replaced periodically. It is estimated that with military small firearms alone, approximately 52,000 barrels are replaced each month.
Several approaches have been proposed to increase the lifetime of the ballistic weapon. One solution has been to encase a leaded bullet within a copper jacket, increasing the melting temperature of the outer layer of the bullet and decreasing deposition of metal within the barrel. However, with high velocity projectiles, the temperature within the barrel approaches the melting point of copper. In these cases, molybdenum disulfide (“MoS2”) coatings are used to protect the copper jacket. However, MoS2 has a large particle size, typically from 10 μm to 35 μm, and does not embed into cracks in the barrel to create a lubricating surface. In addition, MoS2 decomposes above a temperature of 315° C. in an oxidizing environment. Since the barrel temperature for low speed rifles easily exceeds 327° C., decomposition of the MoS2 occurs, producing MoO2, MoC, and Mo.
Hexagonal boron nitride (“h-BN”) has also been used as a ballistic conditioner. As disclosed in U.S. Pat. No. 6,576,598 to Brown, a coating of h-BN, graphite, tungsten disulfide, antimony trioxide, mica, talc, or mixtures thereof is applied to a firearm, firearm component, firearm ammunition, or ammunition element. The h-BN is purchased from a supplier. U.S. Pat. No. 7,197,986 to Calkins discloses applying a dry ceramic lubricant to a gun barrel or a bullet. The dry ceramic lubricant is an h-BN powder. In addition, cubic boron nitride (“c-BN”), which is an abrasive material, has been used to pressure lap gun barrels. As disclosed in U.S. Pat. No. 5,378,499 to Martin et al., c-BN is applied to a bullet. The coated bullet is fired through a gun barrel to remove dimensional variations and roughness in the bore of the gun.
While h-BN coated projectiles or coated barrels have been proposed to increase the lifetime of the barrel, the h-BN has a relatively large particle size and does not penetrate into cracks in the barrel. As such, the h-BN coating provides, at best, lubrication as the projectile exits the barrel. Therefore, it would be desirable to produce a coating that provides lubrication and metal healing properties to the barrel or other metal article.